(1) the
language is a joke or vanity project [...]
For example, it would be bad to have a Klingon Wikipedia, I think.
I totally don't get this. You call Klingon a "joke project" when it has
a strong following, widespread enthusiasm, a complete grammar and
vocabulary, etc., but then you allow something like Toki Pona, which is
hardly even a language and arouses interest solely by being very much
indistinguishable from a joke.
Considering how difficult Klingon is, and how easy Toki Pona is, I believe the number of
Toki Pona speakers already gets close to the number of Klingon speakers (and is probably
growing more). Toki Pona is not just a joke, but rather a conlang linked to a certain
ideology (a kind of Taoism).
I wouldn't reject Klingon on the basis of it being spoken little, or it being a joke,
but I think there are copyright issues about it (though I'm not an expert on that).
Anyway, I personally believe that for a conlang to be accepted in Wikipedia, it should be
proved that at least three people know it (and hopefully some more can at least understand
a bit), so that Wikipedia doesn't get misused for promoting completely personal
conlangs. (Damn, that's going to affect my conlang Logli, but never mind.)
Additionally, copyright issues should be checked out in advance.
Marcos